Means for automatic control of batching when casting from a heat-retaining of casting furnace or ladle (crucible)

ABSTRACT

For the automatic control of batching when casting from a heatretaining furnace or ladle, an arrangement is provided for tapping the ladle in batches into a batching ladle. An arrangement is provided for weighing the batching ladle and the output signal of the weighing arrangement is fed to a deriving device which gives an output signal dependent on the melt flow. The output signal of the deriving device is fed to a comparison device along with a signal representing a desired value. A control device for the tapping of the furnace is combined with the output signal of the comparison device to terminate tapping when a predetermined quantity of melt has been tapped.

Umted States Patent 11 1 1111 3,834,587 Bengt et a1. Sept. 10, 1974 [54]MEANS FOR AUTOMATIC CONTROL OF 2,772,455 12/1956 Easton et a1. .1164/155 BATCHING WHE CASTING FROM A 2,882,567 4/1959 Deakins et a1.222/166 X HEAT-RETAINING 0F CASTING FURNACE 232331323 3/132333123235219133: "61111333112 OR LADLE (CRUCIBLE) 3,457,985 7/1969 Wilson164/155 [75 Inventors: Fredrikson B Bergman Kiel], 3,537,505 11/1970Thalmann 164/155 X both of Vasteras, Sweden Primary Examiner-Robert B.Reeves Asslgnee: Aumanna Sven-Ska Elekmska Assistant Examiner-David A,Scherbel Aktiebolaget, Vasteras, Sweden 22 Filed: Nov. 13, 1972 [57]ABSTRACT [21] AppL NO: 305 684 For the automatic control of batchingwhen casting from a heat-retaining furnace or ladle, an arrangement isprovided for tapping the ladle in batches into a Forelgn ApphcatlonPriority t batching ladle. An arrangement is provided for weigh- Dec.18, 1971 Sweden [4738/71 ing the batching ladle and the output signal ofthe weighing arrangement is fed to'a deriving device [52] US. Cl..-222/56, 164/155, 222/77 which gives an output signal dependent on themelt [51] Int. Cl B22d 37/00 flow. The output signal of the derivingdevice is fed to [58] Field of Search 222/ 166, 14, 16, 56, 77, acomparison device along with a signal representing a 222/DIG. l5, DIG.12; 164/4, 154, 155 desired value. A control device for the tapping ofthe furnace is combined with the output signal of the com- [56]References Cited parison device to terminate tapping when a predeter-UNITED STATES PATENTS mined quantity of melt has been tapped.

2,768,413 10/1956 Alexanderson 164/155 4 Claims, 9 Drawing Figures 3/ 2532 27 33 26 1 tai ng" 47 -1? {j W5 v I 37. "8

48 I 1 7 517 78" I W 1 l //l l 36 .,&L L

\ -1 I 12 1 4 P M W 20 22 PATENIE SEH 01914 834,587

SHEET 2 [If 3 Fig2 I MEANS FOR AUTOMATIC CONTROL OF BATCI'IING WHENCASTING FROM A HEAT-RETAINING OF CASTING FURNACE OR LADLE (CRUCIBLE)BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to a means for automatic control of batching orproportioning when casting from a heat-retaining or casting furnace orladle (crucible).

A pressure casting method of this kind is shown in ASEAs brochureAUl0-103 PRESSPOUR casting m -J a.

2. Description of the PrioFArt For control of the flow from the furnaceor the ladle during automatic batching, previously among other thingslevel indicators for the melt have been used, placed in the tappingspout of the furnace and/or in the moulding box or the casting device.Such level indicators, for example those which are placed on themoulding box, involve the disadvantage that a rising gate has to bearranged which, among other things, causes expense for exchange ofdeteriorated material. In other words, certain parts of the casting bodyhave to be cast, and these must be removed later on in order to obtain asignal from the level indicator. Such level indicators of on-off typealso involve a problem concerning the accuracy when casting, and alsotheir reliability in operation has been a problem. Indicators with aproportional signal have also been a problem.

It has also been tried to cast on the basis of time. In these cases anapproximately constant flow has been used and the time has beenmeasured. After a certain tapping time, the tapping has beeninterrupted, and then it has been possible to count on there being acertain fixed batch in the pouring ladle or casting device. Also thishas involved certain drawbacks, and often a bad material exchange.Weight control at the casting ladle has also been used, and at a certainsignal the casting has been interrupted, but a disadvantage of thesedevices is that after the interruption an extra amount has been obtainedin the pouring ladle, corresponding to the time constant and the meltquantity in the spray. Furthermore, the stoppage in casting has takenplace quite abruptly, causing overproportioning and wastage and otherinconvenience. All these previously known devices have therefore as arule required supervision by an operator. It is desirable that theconditions should be constant during the batching, independent of thefilling degree of the furnace, but so far this has been difficult toachieve.

SUMMARY OF THE INVENTION The invention aims at a solution to these andrelated problems and is characterised in that the furnace is arranged tobe tapped in batches into a batching ladle which is provided with weightequipment, the output signal of whichis fed to a deriving device inorder to obtain an output signal dependent on the melt flow, said signalbeing arranged to be transmitted together with a signal for the desiredvalue to a comparison device, the output signal of which is arranged tocontrol the tapping from the furnace and other factors. In this way, asignal is obtained, acting as a control signal and being directlydependent on the flow, and it is possible,

for example, to slacken the tapping before the batching ladle iscompletely filled and stop the tapping just at the right moment. Themelt content in the flow being tapped can also be taken intoconsideration. Thus, an exact batching control is obtained withoutappreciable wastage of material and without supervision being necessary. Such a means is easily fitted into an automatic production linefor such cast products.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is exemplified in theaccompany drawings, of which FIG. 1 shows a skeleton diagram used for apressure casting furnace of channel type. FIG. 2 shows the filling andemptying conditions during batching with one batching ladle, FIG. 3 thecorresponding condition when using two batching ladles and FIG. 4 thesame for four batching ladles. FIG. 5 shows a gearing device for thetare in case of small tare weight, and FIG. 6 shows the same device seenfrom the side. FIG. 7 shows the devices for weighing the tare arrangedin accordance with FIG. 5, and FIGS. 8 and 9 alternative solutions ofthe gearing of the tare.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a furnace ofsubmerged resistor type (channel-type induction furnace) ll of tea-pottype having separate inlets 12 and outlets 13 and a furnace hearthclosed by means of a liquid lock, said furnace being provided with oneor several inductors of channel type. A tapping spout 15 is arranged atthe outlet, through which melt from the furnace is to be supplied to abatching ladle 16 in suitable batches, and this batching ladle can bearranged together with other similar means on a rotatable base on aso-called turning head system (see the small figure to the left in FIG.4). When more batching ladles are used, these can also be arranged onthe turning head system. When the ladle 16 has been filled with asuitable quantity of melt, it can be teemed into a funnel or mould 17which, in turn, is to be emptied into a flank or mould 27 on anautomatic casting line or moulding machine, type DISAMATIC.

The weight of the batching ladle (W-l-tare) is arranged to be measuredin a suitable manner, for example by means of a magnetostrictivemeasuring device of the type shown in Swedish patent specification151,267, see detail .19 in the present FIG. I, and the tare (the weightof empty batching ladle 16) is arranged to be measured when the batchingladle after emptying returns to position for filling and affects asensing device at 21, preferably in a similar way, and the measuringsignal for the tare is transmitted to a calculating device or computer20, where the tare signal is then subtracted from the gross weight inorder to obtain a signal for the net weight (W), said signal being thenderived in order to obtain a signal proportional to the flow (W thederivate of the net weight). The batching ladle 16 is tiltable by meansof a suitable drive means, such as a hydraulic device 18, where theteeming rate can be controlled with a programming device in order toobtain a favorable flow at the beginning and end. At the batching ladle,inoculation with, for example, ferrosilicon is automatically carriedout.

The computer 20 is connected to an indicating device 22 of digital orother type, and at the desk 23 the information to be indicated at 22 canbe fed, such as batch weight, total weight, tare weight, flow, remainingmelt in the furnace and so on. The furnace II can also be tiltable andpossibly of crucible or of other type and provided with a heat-retainingmember.

At the desk 23 the desired batch weight can be fed at a certain castingline, and the batch weight should be independent of the degree offilling of the furnace 11.

At 31 a ramp device is arranged, from which a suitable desired value forthe flow (W) reference flow can be obtained, said value beingtransmitted to an addition device 25 together with the signal for actualvalue W for the flow. The signal for flow deviation (from 25) istransmitted to a flow regulator 32, preferably a control amplifier ofproportional, integrating type. Output signals for this amplifier 32will, as appears below, constitute a reference for the pressure control(the pressure tapping of the furnace 11), and this signal is transmittedto a second addition device 27, together with a signal corresponding tothe pressure 28 measured above the melt in the furnace. The pressuresignal is also transmitted over a motor driven potentiometer 34,constituting a memory circuit" for the pressure during the tapping whichis not constant during the whole emptying process but varies accordingto a certain curve. The output signal from the potentiometer 34 istransmitted, after switching on at the end of the filling, to the sameaddition device 27, and error signals (deviations from desired pressurein the furnace degree of tapping) are transmitted to a pressure controlamplifier 33, the output signal of which is transmitted to an adjustingdevice for the pressure in the furnace (air or inert gas, transmitted at14).

It is desirable, as appears from FIG. 2, when using one batching ladle16, to allow the flow rate W (F S) to increase first along a slopingcurve, and then to be held constant until a certain directional signal Whas been attained, after which the flow is to be slackened to a certainweight W where the tapping is to be discontinued. (At W the tapping isto be switched from W to W T shows then the emptying of the batchingladle and F the filling which again follows. W shows in FIG. 2 when thefinal weight is to be attained, and N is the level in the furnace andhow this changes with the time t.

FIG. 3 shows how the emptying (T) and filling (F) scheme can be arrangedwhen two ladles (1,2) are used, and FIG. 4 shows the same for fourladles (1,2,3,4). To the left in FIG. 4 is shown how the ladles areturned in the direction of the arrow for emptying (T) and filling (F) onthe turning head system.

W and W (FIG. 1) are adjusted at the computer 20, and on attaining W forone batch the relay coil 29 receives current and its contact 29 closesthe circuit W to the ramp device after W has been switched onpreviously. A filling scheme according to FIG. 2 is obtained until W hasbeen attained, when the relay coil 48 receives current and, among otherthings, its contact 48 breaks and the flow control ceases. The referencedevice 34 is switched on by means of the contact 48" and takes over thecontrol as well the pressure reduction reference A P.

The supervision now comprises a photocell device 49, the output signalof which is transmitted to an integrating amplifier 36 which, after coil48 has received current, also causes contact 48" to feed the additiondevice 27. The integration time for the amplifier 36 is selected so thatmaximum filling rate is accomplished with no risk of running over. A Pis the desired pressure reduction during tapping of a batch.

In order to avoid undesirable disturbances when starting up after atapping process (see FIG. 2 the second time F occurs), a circuit 37 isswitched on, arranged in such a way that the output signal from the flowcontrol 32 corresponds to the current pressure during tapping (bump-lessfunction).

The control amplifier 37 is arranged to transmit a signal to theaddition device 25 over contact 48"" (closed when the coil 48 receivescurrent), in this way affecting the output signal of the flow control sothat it corresponds to the current pressure when starting up.

In FIG. 5 is shown how the taring control can be ar ranged for smalltares. The ladle is located at the end of a lever 51, or supported at apoint 54 and rotatable by means of a motor 53 for tapping through thegear drive 52. See also FIG. 6 where the same process is shown seenlaterally. In FIG. 7 is shown how the shaft 51 is arranged on a fixedlysupported revolving axle 54 in which the balance devices 19 arearranged. FIG. 8 shows how the balance device is arranged at 19, saidbalance device emitting a suitable signal corresponding to the tare,which signal can also be obtained in the case of very small tareweights. FIG. 9 shows an alternative, the balance device being locatedbelow a pivot for a shaft, at the end of which the ladle is positioned.

To sum up, the advantages of this invention can be said to be thefollowing:

Controlled tapping rate, which means that a maximum proportioning ratecan be maintained during the major part of the tapping process. The flowrate is determined by deriving the weight signal, and therefore noparticular sensing member for the flow rate itself is needed. The demandon accuracy for the flow control is moderate, since the total weightfinally decides when the tapping is to cease.

Controlled metal weight in the batching ladle prior to casting. Sinceclose tolerances can be kept, essential savings as to material costs canbe made.

When the tapping is finished, the level in the tapping channel islowered to a position on a level with the dam for the tapping spout 15,independent of the degree of filling of the furnace 11. This means,aside from time saving, that the consumption of the pressure gas in thefurnace hearth (the furnace tank) is reduced to a minimum. The latter isparticularly advantageous when casting nodular iron.

Filling of the furnace can be made irrespective of whether tapping isgoing on or not.

The system can be fully automated.

The system makes possible continuous casting on a casting line. Whenapplying the turning head system and/or oscillating batching ladle 16,casting can be carried out without having to stop the casting line.

The arrangements exemplified above can be varied in many ways within thescope of the following claims.

We claim:

1. Means for automatic control of batching when casting from a crucibleincluding a batching ladle, means for tapping the crucible in batchesinto the batching ladle, means for weighing the batching ladle, aderiving device, means for feeding the output signal of the batchingladle weighing means to the deriving device, means in the derivingdevice to transform the output signal of the batching ladle weighingmeans, which output signal depends upon the weight of batches of thetapped melt, into the derivative of the output signal of the batchingladle weighing means, the derivative of the output signal of theweighing means representing the rate of the melt flow out of thecrucible, a reference device providing signals representing the desiredvalue of melt flow rate out of the crucible, means responsive to theoutput signal of the batching ladle weighing means to change the outputsignal of the reference device, a comparison device, means to feed tothe comparison device the signal from the reference device and theoutput signal from the deriving means, a control device for the tappingof the crucible, and means to feed to the control device output signalsfrom the comparison device to control the tapping rate to maintain it atdifferent values in response to differences in the weight of thebatching ladle.

2. Means according to claim 1, in which the crucible is a furnace ofsubmerged resistor type provided with separate inlets and outlets andwith an inflow for pressure medium at the hearth in order to control thetapping.

3. Means according to claim 2, in which a level measuring device isarranged at the outflow of the furnace and means responsive to theoutput signal of said level measuring device for controlling thepressure in the furnace.

4. Means according to claim 1, which includes means to measure the tarewhen the ladle is empty, a subtraction device, and means to feed theoutputs of the tare measuring means to said subtraction device togetherwith the output signalof the weighing means.

1. Means for automatic control of batching when casting from a crucibleincluding a batching ladle, means for tapping the crucible in batchesinto the batching ladle, means for weighing the batching ladle, aderiving device, means for feeding the output signal of the batchingladle weighing means to the deriving device, means in the derivingdevice to transform the output signal of the batching ladle weighingmeans, which output signal depends upon the weight of batches of thetapped melt, into the derivative of the output signal of the batchingladle weighing means, the derivative of the output signal of theweighing means representing the rate of the melt flow out of thecrucible, a reference device providing signals representing the desiredvalue of melt flow rate out of the crucible, means responsive to theoutput signal of the batching ladle weighing means to change the outputsignal of the reference device, a comparison device, means to feed tothe comparison device the signal from the reference device and theoutput signal from the deriving means, a control device for the tappingof the crucible, and means to feed to the control device output signalsfrom the comparison device to control the tapping rate to maintain it atdifferent values in response to differences in the weight of thebatching ladle.
 2. Means according to claim 1, in which the crucible isa furnace of submerged resistor type provided wiTh separate inlets andoutlets and with an inflow for pressure medium at the hearth in order tocontrol the tapping.
 3. Means according to claim 2, in which a levelmeasuring device is arranged at the outflow of the furnace and meansresponsive to the output signal of said level measuring device forcontrolling the pressure in the furnace.
 4. Means according to claim 1,which includes means to measure the tare when the ladle is empty, asubtraction device, and means to feed the outputs of the tare measuringmeans to said subtraction device together with the output signal of theweighing means.